Display device and method for manufacturing display device

One embodiment of the present invention relates to a display device. One embodiment of the present invention relates to a method for manufacturing a display device.

Note that one embodiment of the present invention is not limited to the above technical field. Examples of the technical field of one embodiment of the present invention disclosed in this specification and the like include a semiconductor device, a display device, a light-emitting apparatus, a power storage device, a memory device, an electronic device, a lighting device, an input device, an input/output device, a driving method thereof, and a manufacturing method thereof. A semiconductor device refers to any device that can function by utilizing semiconductor characteristics.

In recent years, higher-resolution display panels have been required. Examples of devices that require high-resolution display panels include a smartphone, a tablet terminal, and a laptop computer. Moreover, higher resolution has been required for a stationary display device such as a television device or a monitor device along with an increase in definition. Furthermore, an example of a device required to have the highest resolution is a device for virtual reality (VR) or augmented reality (AR).

Examples of a display device that can be used for a display panel include, typically, a liquid crystal display device, a light-emitting apparatus including a light-emitting element such as an organic EL (Electro Luminescence) element or a light-emitting diode (LED), and electronic paper performing display by an electrophoretic method or the like.

For example, the basic structure of an organic EL element is a structure in which a layer containing a light-emitting organic compound is provided between a pair of electrodes. By applying voltage to this element, light emission can be obtained from the light-emitting organic compound. A display device using such an organic EL element does not need a backlight that is necessary for a liquid crystal display device and the like; thus, a thin, lightweight, high-contrast, and low-power display device can be achieved. Patent Document 1, for example, discloses an example of a display device using an organic EL element.

An object of one embodiment of the present invention is to provide a display device that can easily achieve higher resolution and a manufacturing method thereof. Another object of one embodiment of the present invention is to provide a display device having both high display quality and high resolution. Another object of one embodiment of the present invention is to provide a display device with high contrast. Another object of one embodiment of the present invention is to provide a highly reliable display device.

An object of one embodiment of the present invention is to provide a display device having a novel structure or a method for manufacturing a display device. Another object of one embodiment of the present invention is to provide a method for manufacturing the above-described display device with a high yield. Another object of one embodiment of the present invention is to at least reduce at least one of problems of the conventional technology.

Note that the description of these objects does not preclude the existence of other objects. Note that one embodiment of the present invention does not have to achieve all the objects. Objects other than these can be derived from the description of the specification, the drawings, the claims, and the like.

One embodiment of the present invention is a method for manufacturing a display device, including a first step of forming a first pixel electrode, a second pixel electrode, and a first electrode; a second step of depositing a first EL film over the first pixel electrode and the second pixel electrode; a third step of forming a first sacrificial film covering the first EL film and the first electrode; a fourth step of exposing the second pixel electrode by etching the first sacrificial film and the first EL film and forming a first EL layer over the first pixel electrode and a first sacrificial layer over the first EL layer and the first electrode; a fifth step of depositing a second EL film over the first pixel electrode and the second pixel electrode; a sixth step of forming a second sacrificial film covering the second EL film and the first electrode; a seventh step of forming a second EL layer over the second pixel electrode and a second sacrificial layer over the second EL layer by etching the second sacrificial film and the second EL film; an eighth step of exposing the first EL layer, the second EL layer, and the first electrode by removing the first sacrificial layer and the second sacrificial layer; a ninth step of forming a common layer over the first EL layer and the second EL layer; and a tenth step of forming a common electrode over and in contact with the common layer and the first electrode.

In the above, the first EL film, the second EL film, and the common layer are preferably formed by an evaporation method using a shielding mask.

In the above, the numbers of the first pixel electrodes and the second pixel electrodes are preferably plural. At this time, it is preferable that the first pixel electrode and the second pixel electrode be arranged in a first direction, and the plurality of first pixel electrodes be arranged in a second direction intersecting the first direction. Moreover, the method preferably includes an eleventh step of removing portions of the common electrode, the common layer, and the first EL layer between the two adjacent first pixel electrodes by etching after the tenth step.

The above method preferably includes a twelfth step of forming an insulating layer between the two adjacent first pixel electrodes between the first step and the second step. Furthermore, it is preferable that in the eleventh step, the common electrode, the common layer, and the first EL layer positioned over the insulating layer be etched and a portion of the insulating layer be etched to form a recessed portion in the insulating layer.

In any of the above, the first sacrificial film and the second sacrificial film preferably contain the same metal film, alloy film, metal oxide film, semiconductor film, or inorganic insulating film. In the fourth step, the first EL film is preferably etched by dry etching using an etching gas not containing oxygen as its main component. Furthermore, in the eighth step, the first sacrificial layer and the second sacrificial layer are preferably removed by wet etching using a tetramethyl ammonium hydroxide aqueous solution, diluted hydrofluoric acid, oxalic acid, phosphoric acid, acetic acid, nitric acid, or a mixed solution thereof. In particular, the first sacrificial film and the second sacrificial film preferably contain aluminum oxide.

Any of the above methods preferably include a thirteenth step of forming a hard mask between the third step and the fourth step be included. Furthermore, it is preferable that in the fourth step, after the first sacrificial film is etched using the hard mask, the hard mask and the first EL film be etched by the same treatment.

In any of the above, each of the first EL layer and the second EL layer is preferably processed into a band-shaped top surface shape.

Any of the above methods preferably include a fourteenth step of forming a protective layer over the common electrode after the tenth step be included.

Another embodiment of the present invention is a display device including a plurality of first light-emitting elements and a plurality of second light-emitting elements. The first light-emitting element includes a first pixel electrode, a first EL layer, a common layer, and a common electrode. The second light-emitting element includes a second pixel electrode, a second EL layer, the common layer, and the common electrode. An insulating layer is included between the two first pixel electrodes, between the two second pixel electrodes, and between the first pixel electrode and the second pixel electrode. The first light-emitting element and the second light-emitting element are arranged in a first direction. The plurality of first light-emitting elements and the plurality of second light-emitting elements are each arranged in a second direction intersecting the first direction. The common layer and the common electrode have a band shape extending in the first direction. The first EL layer, the common layer, and the common electrode include an end portion overlapping with the insulating layer between the two adjacent first pixel electrodes.

According to one embodiment of the present invention, a display device that can easily achieve higher resolution and a manufacturing method thereof can be provided. A display device having both high display quality and high resolution can be provided. A display device with high contrast can be provided. A highly reliable display device can be provided.

According to one embodiment of the present invention, a display device having a novel structure or a method for manufacturing a display device can be provided. A method for manufacturing the above-described display device with a high yield can be provided. According to one embodiment of the present invention, at least one of problems of the conventional technology can be at least reduced.

Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not need to have all the effects. Effects other than these can be derived from the description of the specification, the drawings, the claims, and the like.

Hereinafter, embodiments will be described with reference to the drawings. Note that the embodiments can be implemented in many different modes, and it will be readily understood by those skilled in the art that modes and details thereof can be changed in various ways without departing from the spirit and scope thereof. Thus, the present invention should not be construed as being limited to the description of the following embodiments.

Note that in structures of the invention described below, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and the description thereof is not repeated. Furthermore, the same hatch pattern is used for the portions having similar functions, and the portions are not especially denoted by reference numerals in some cases.

In each drawing described in this specification, the size, the layer thickness, or the region of each component is exaggerated for clarity in some cases. Therefore, they are not limited to the illustrated scale.

In this specification and the like, the ordinal numbers such as “first” and “second” are used in order to avoid confusion among components and do not limit the number.

In this specification and the like, the term “film” and the term “layer” can be interchanged with each other. For example, in some cases, the term “conductive layer” and the term “insulating layer” can be interchanged with the term “conductive film” and the term “insulating film”, respectively.

Note that in this specification, an EL layer means a layer containing at least a light-emitting substance (also referred to as a light-emitting layer) or a stacked-layer body including the light-emitting layer provided between a pair of electrodes of a light-emitting element.

In this specification and the like, a display panel that is one embodiment of a display device has a function of displaying (outputting) an image or the like on (to) a display surface. Therefore, the display panel is one embodiment of an output device.

In this specification and the like, a substrate of a display panel to which a connector such as an FPC (Flexible Printed Circuit) or a TCP (Tape Carrier Package) is attached, or a substrate on which an IC is mounted by a COG (Chip On Glass) method or the like is referred to as a display panel module, a display module, or simply a display panel or the like in some cases.

Described in this embodiment are a structure example of a display device of one embodiment of the present invention and an example of a manufacturing method of the display device.

One embodiment of the present invention is the display device including a light-emitting element (also referred to as a light-emitting device). The display device includes at least two light-emitting elements which emit light of different colors. The light-emitting elements each include a pair of electrodes and an EL layer therebetween. The light-emitting elements are preferably organic EL elements (organic electroluminescent elements). The two or more light-emitting elements emitting different colors include respective EL layers containing different materials. For example, three kinds of light-emitting elements emitting red (R) light, green (G) light, and blue (B) light are included, whereby a full-color display device can be achieved. Here, as a way of forming EL layers separately between light-emitting elements of different colors, an evaporation method using a shadow mask such as a metal mask is known. However, this method causes a deviation from the designed shape and position of an island-shaped organic film due to various influences such as the low accuracy of the metal mask, the positional deviation between the metal mask and a substrate, a warp of the metal mask, and the vapor-scattering-induced expansion of outline of the deposited film; accordingly, it is difficult to achieve high resolution and a high aperture ratio of the display device. Thus, a measure has been taken for pseudo improvement in resolution (also referred to as pixel density) by employing a unique pixel arrangement method such as a PenTile arrangement, for example.

In one embodiment of the present invention, fine patterning of an EL layer is performed without a shadow mask such as a metal mask. Thus, a display device that has high resolution and a high aperture ratio, which has been difficult to achieve, can be achieved. Moreover, EL layers can be formed separately, enabling the display device to perform extremely clear display with high contrast and high display quality.

In this specification and the like, a device formed using a metal mask or an FMM (a fine metal mask, a high-resolution metal mask) may be referred to as a device having an MM (a metal mask) structure. In this specification and the like, a device formed without using a metal mask or an FMM may be referred to as a device having an MML (metal maskless) structure.

Here, description is made on a case where EL layers in light-emitting elements of two colors are separately formed, for simplicity. First, a stack of a first EL film and a first sacrificial film is formed to cover two pixel electrodes. Next, a resist mask is formed over the first sacrificial film in a position overlapping with one pixel electrode (a first pixel electrode). Then, the resist mask, part of the first sacrificial film, and part of the first EL film are etched. At this time, the etching is stopped when the other pixel electrode (a second pixel electrode) is exposed. Thus, part of the first EL film processed into a band shape or an island shape (also referred to as a first EL layer) can be formed over the first pixel electrode, and part of the sacrificial film (also referred to as a first sacrificial layer) can be formed thereover.

Next, a stack of a second EL film and a second sacrificial film is formed. Then, a resist mask is formed in a position overlapping with the second pixel electrode. Then, the resist mask, part of the second sacrificial film, and part of the second EL film are etched in a manner similar to the above. As a result, the first EL layer and the first sacrificial layer are provided over the first pixel electrode, and a second EL layer and a second sacrificial layer are provided over the second pixel electrode. In this manner, the first EL layer and the second EL layer can be formed separately. Finally, the first sacrificial layer and the second sacrificial layer are removed to expose the first EL layer and the second EL layer, and then a common electrode is formed, so that the light-emitting elements of two colors can be formed separately.

Furthermore, by repeating the above-described steps, EL layers in light-emitting elements of three or more colors can be formed separately. Accordingly, a display device including light-emitting elements of three colors or four or more colors can be achieved.

Here, an electrode (also referred to as a first electrode, a connection electrode, or the like), which is to supply a potential to the common electrode, can be formed on the same plane as the pixel electrode to be electrically connected to the common electrode. The connection electrode is positioned outside the display region where the pixels are provided. In order to prevent a top surface of the connection electrode from being exposed to etching of the first EL film, it is preferable that the first sacrificial layer be also provided over the connection electrode. Also in etching of the second EL film, the second sacrificial layer is preferably provided over the connection electrode. The first sacrificial layer and the second sacrificial layer provided over the connection electrode can be removed by etching concurrently with etching of the first sacrificial layer over the first EL layer and the second sacrificial layer over the second EL layer.

It is difficult to set the distance between the EL layers of different colors to be less than 10 μm with a formation method using a metal mask, for example; however, with use of the above method, the distance can be narrowed to be less than or equal to 3 μm, less than or equal to 2 μm, or less than or equal to 1 μm. For example, with use of a light exposure apparatus for LSI, the distance can be narrowed to be less than or equal to 500 nm, less than or equal to 200 nm, less than or equal to 100 nm, or less than or equal to 50 nm. Accordingly, the area of a non-light-emitting region that may exist between two light-emitting elements can be significantly reduced, and the aperture ratio can be close to 100%. For example, the aperture ratio lower than 100% but higher than or equal to 50%, higher than or equal to 60%, higher than or equal to 70%, higher than or equal to 80%, or higher than or equal to 90% can be achieved.

Furthermore, a pattern of the EL layer itself can be made much smaller than that in the case of using a metal mask. For example, in the case of using a metal mask for forming EL layers separately, a variation in the thickness of the pattern occurs between the center and the edge of the pattern. This causes a reduction in an effective area that can be used as a light-emitting region with respect to the entire pattern area. By contrast, in the above manufacturing method, a pattern is formed by processing a film deposited to have a uniform thickness, which enables a uniform thickness in the pattern. Thus, even with a fine pattern, almost the entire area can be used as a light-emitting region. Therefore, the above manufacturing method can achieve both high resolution and a high aperture ratio.

In this manner, the above manufacturing method can provide a display device in which minute light-emitting elements are integrated, and it is not necessary to conduct a pseudo improvement in resolution by employing a unique pixel arrangement method such as a PenTile arrangement. Thus, the display device can achieve resolution higher than or equal to 500 ppi, higher than or equal to 1000 ppi, higher than or equal to 2000 ppi, higher than or equal to 3000 ppi, or higher than or equal to 5000 ppi while having what is called a stripe arrangement where R, G, and B are arranged in one direction.

More specific structure examples and manufacturing method examples of the display device of one embodiment of the present invention are described below with reference to drawings.

illustrates a schematic top view of a display deviceof one embodiment of the present invention. The display deviceincludes a plurality of light-emitting elementsR exhibiting red, a plurality of light-emitting elementsG exhibiting green, and a plurality of light-emitting elementsB exhibiting blue. In, light-emitting regions of the light-emitting elements are denoted by R, G, and B to easily differentiate the light-emitting elements.

The light-emitting elementsR, the light-emitting elementsG, and the light-emitting elementsB are arranged in a matrix.illustrates what is called a stripe arrangement, in which the light-emitting elements of the same color are arranged in one direction. Note that the arrangement method of the light-emitting elements is not limited thereto; another arrangement method such as a delta arrangement, a zigzag arrangement, or a PenTile arrangement may also be used.

The light-emitting elementsR, the light-emitting elementsG, and the light-emitting elementsB are arranged in the X direction. The light-emitting elements of the same color are arranged in the Y direction intersecting with the X direction.

As the light-emitting elementsR, the light-emitting elementsG, and the light-emitting elementsB, an organic EL element such as an OLED (Organic Light Emitting Diode) or a QLED (Quantum-dot Light Emitting Diode) is preferably used. As a light-emitting substance contained in the EL element, a substance that emits fluorescence (a fluorescent material), a substance that emits phosphorescence (a phosphorescent material), an inorganic compound (e.g., a quantum dot material), a substance that exhibits thermally activated delayed fluorescence (a thermally activated delayed fluorescent (TADF) material), and the like can be given.

is a schematic cross-sectional view taken along dashed-dotted line A-Ain.is a schematic cross-sectional view taken along dashed-dotted line B-B.

illustrates a cross section of the light-emitting elementR, the light-emitting elementG, and the light-emitting elementB. The light-emitting elementR includes a pixel electrodeR, an EL layerR, an EL layer, and a common electrode. The light-emitting elementG includes a pixel electrodeG, an EL layerG, the EL layer, and the common electrode. The light-emitting elementB includes a pixel electrodeB, an EL layerB, the EL layer, and the common electrode. The EL layerand the common electrodeare shared by the light-emitting elementR, the light-emitting elementG, and the light-emitting elementB. The EL layercan also be referred to as a common layer.

The EL layerR included in the light-emitting elementR contains at least a light-emitting organic compound that emits light with intensity in a red wavelength range. The EL layerG included in the light-emitting elementG contains at least a light-emitting organic compound that emits light with intensity in a green wavelength range. The EL layerB included in the light-emitting elementB contains at least a light-emitting organic compound that emits light with intensity in a blue wavelength range.

The EL layerR, the EL layerG, and the EL layerB may each include one or more of an electron-injection layer, an electron-transport layer, a hole-injection layer, and a hole-transport layer in addition to the layer containing a light-emitting organic compound (the light-emitting layer). The EL layercan have a structure that does not include the light-emitting layer. For example, the EL layerincludes one or more of an electron-injection layer, an electron-transport layer, a hole-injection layer, and a hole-transport layer.

The pixel electrodeR, the pixel electrodeG, and the pixel electrodeB are provided for the respective light-emitting elements. Each of the common electrodeand the EL layeris provided as a continuous layer shared by the light-emitting elements. A conductive film that transmits visible light is used for the pixel electrodes or the common electrode, and a reflective conductive film is used for the other. The use of the light-transmitting pixel electrodes and the reflective common electrodeoffers a bottom-emission display device whereas the use of the reflective pixel electrodes and the light-transmitting common electrodeoffers a top-emission display device. Note that when both the pixel electrodes and the common electrodetransmit light, a dual-emission display device can be obtained.